U.S. Pat. No. 3,494,956 discloses that dehydrodimerization products of propene, isobutene, toluene, methyl styrene, acetonitrile, and acetic acid may be obtained by allowing substances to react with oxygen in the vapour phase at temperatures of over 300.degree.C and in the presence of lead oxide and/or cadmium oxide, and/or thallium oxide. However, in the presence of optimum reaction conditions, considerable amounts of starting materials in this known process will react with the oxygen present to form carbon dioxide, with adverse affects on yields of products.
U.S. patent application Ser. No. 812,415, filed Apr. 1, 1969 now abandoned discloses that propene, toluene, and acetic acid, and the like, may be converted into their respective dehydrodimerization products by oxidative coupling in the presence of a regeneratable reagent containing oxygen, e.g. bismuth trioxide, in the absence of oxygen. In the coupling reaction, the oxygen of the regeneratable reagent is consumed, so that the exhausted reagent must be regenerated by oxidation in the absence of organic starting material.
In this known process, it is necessary to employ a carrier (alundum, silica, carborundum, dolomite, zirconia, alumina) which has a small specific surface area, preferably smaller than 1 m.sup.2 /g, as the reaction will, otherwise, proceed with little selectively.
It has now been found that the above-mentioned dehydrodimerization products may be obtained in high yields by oxidative coupling in the absence of oxygen gas, if the catalyst to be used is supported on a basic carrier with a large surface area.